1. Field of the Invention
The present invention relates to a magnetic recording medium having improved orientation degree and maximum residual magnetic flux density. More particularly, it relates to a magnetic recording medium comprising vinyl chloride-vinyl acetate-maleic acid copolymer having a content of maleic acid component of at least 1.5% as a component of a binder for a magnetic layer.
2. Description of the Prior Arts
The magnetic recording media such as magnetic tapes and magnetic cards are usually prepared by forming a magnetic layer on a substrate such as a film made of polyvinyl chloride, polyester or polycarbonate by bonding a magnetic powder such as .gamma.-Fe.sub.2 O.sub.3 with a binder. Various magnetic recording media have been proposed.
Recently, higher characteristics as improvement of electromagnetic convertible characteristic and higher recording density have been further required depending upon an increase of fields of usages of such magnetic recording media.
Certain vinyl chloride type copolymers have been used as the binder for this purpose. Vinyl chloride-vinyl acetate copolymers have been usually used because of high miscibility to a rubber type binder and high dispersibility. However, the vinyl chloride-vinyl acetate copolymers have not a functional group whereby it is not easy to improve dispersibility of the magnetic powder in the magnetic layer and it is not easy to react it by a thermosetting reaction. It has been proposed to use vinyl chloride-vinyl acetate-vinyl alcohol copolymers instead of the vinyl chloride-vinyl acetate copolymers. Because of hydroxyl groups in the copolymer, the dispersibility to the magnetic powder is improved and the thermosettable reaction is performed. However, because of vinyl alcohol component, a glass transition point of the copolymer is disadvantageously high to be difficult for improving surface property by a calender processing.